Method for operating a multi-gas burner and a multi-gas burner

ABSTRACT

The invention relates to a method for operating a multi-gas burner having at least one burner lance with a first, second and third nozzle and having a first, second and a third feed chamber. It is provided according to the invention that for high-calorific operation air is fed via the first nozzle, O 2 -depleted gas via the second nozzle and the high-calorific combustion gas via the third nozzle into the combustion chamber, where they are combusted. Furthermore the invention relates to a multi-gas burner for operation with a low-calorific and a high-calorific combustion gas.

The invention relates to a method for operating a multi-gas burner and to a multi-gas burner for operation with a low-calorific and a high-calorific combustion gas.

Generic multi-gas burners have in most cases a combustion chamber and at least one burner lance. This burner lance is designed with a first, a second and a third nozzle. Furthermore a first, a second and a third feed chamber are provided which are each connected in terms of flow to a respective nozzle for feeding gases into the combustion chamber. The nozzles of the at least one burner lance end on one side in the combustion chamber and on the other side in a respective feed chamber. Furthermore a burner muffle is provided in the combustion chamber in the region of the end of the nozzles. A burner with a plurality of burner lances is described as a multiple lance burner.

Generic burners are known for example from DE 196 27 203 C2 and DE 42 08 951 C2.

Such gas burners are used in hot gas generators which are used to heat process gases, for example within the scope of smelting iron ores. Hot process gases are required for a grinding-drying process of coal. The ground and dried coal is further used in the smelting of iron ores. As combustion gases for hot gas generators generally low-calorific gases—also described as lean gases—are fed with an oxygen carrier for combustion, in particular air, through the nozzles into the combustion chamber, where they are then mixed with the oxygen carrier, ignited and combusted.

In order to increase the flexibility and usability of hot gas generators it is desirable to also be able to alternatively operate the burner(s) of the hot gas generators with other combustion gases such as high-calorific combustion gases.

Due to the higher calorific value of the high-calorific combustion gases they combust with a higher flame temperature in comparison with the low-calorific gases. It is hereby to be considered that, with effect from combustion temperatures above approximately 1300° C., NO_(x) is formed through a thermal conversion of the N₂ of the oxygen carriers for the combustion, particularly with normal air. When using high-calorific combustion gases the combustion temperatures usually lie above this critical temperature range. The formation of NO_(x) must, however, be extensively avoided in accordance with environmental protection legislation.

It is thus an object of the invention to indicate a method for operating a multi-gas burner and such a multi-gas burner, with which the combustion of high-calorific combustion gases is possible while at the same time complying with applicable environmental protection legislation, in particular in combination with coal grinding plants.

This object is achieved according to the invention through a method for operating a mul-ti-gas burner having the features of claim 1 and a multi-gas burner having the features of claim 10.

Further advantageous embodiments are indicated in the dependent claims, the descrip-tion and the figures.

It is provided according to claim 1 that a multi-gas burner having at least one burner lance with a first, a second and a third nozzle, having a first, a second and a third feed chamber, which are each connected in terms of flow to a respective nozzle, and having a combustion chamber, into which the at least one burner lance projects, is operated in such a way that in high-calorific operation air is introduced via the first nozzle and, simultaneously, O₂-depleted gas is introduced via the second nozzle and a high-calorific combustion gas is introduced via the third nozzle into the combustion chamber, where they are reacted, in particular combusted, the air and the O₂-depleted gas being used as oxygen providers or oxygen carriers for combustion.

The invention is based upon the recognition that in order to avoid the formation of NO_(x) it is necessary to reduce the flame temperature in such a way that it lies below a range, in which the greatest amounts of NO_(x) can be produced. This temperature range lies below approximately 1300° C.

This can be achieved according to the invention in that the combustion is carried out with increased λ values in comparison with a low-calorific operation, that is to say a combustion of a low-calorific combustion gas. The λ value is also described as the combustion ratio or air ratio and defines the ratio of oxygen providers supplied for combustion, in particular air, to the minimum air quantity stoichiometrically required for the combustion of the combustion gas.

If when combusting a high-calorific gas the combustion is carried out with more combustion air, thus with a greater quantity of oxygen providers for the combustion, the λ value increases. By additionally introducing more combustion air the gases produced are cooled in case of complete combustion of the combustion gas. It can hereby be achieved that the whole combustion process takes place at a temperature lying below the critical temperature range for NO_(x) production.

Normal ambient air with an oxygen content of approximately 21% is conventionally used for the oxygen provider for the combustion. Due to the higher quantity of the oxygen provider for the combustion the oxygen content in the hot process gas increases. This is problematic particularly when the gas burner is used in a hot gas generator which is used to produce process gases for coal grinding plants. Such coal grinding plants are used for example for the processing of carbon carriers such as hard coals, for blowing into blast furnaces using the pulverised coal injection (PCI) method or within the scope of coal gasification plants. In such plants the process gas must have an oxygen content of less than 10% for the purpose of explosion protection. It is not therefore possible to facilitate the use of high-calorific combustion gases by increasing the λ value. The same problem exists with many process gases which are used in explosion-risk environments. It is thus compulsorily necessary when using high-calorific combustion gases to not only prevent NO_(x) but also to ensure that the hot process gas produced has an oxygen content lying below a percentage content fixed in dependence upon the process.

A further core idea of the invention can therefore be seen in not using exclusively normal air as an oxygen provider for combustion but instead mixing the oxygen provider for the combustion from normal air and O₂-depleted gas. This results in the oxygen provider used for the combustion having an overall lower oxygen content than normal air. The burner can hereby be operated with higher λ values so that the previously described necessary reduction in the flame temperature is facilitated. Through the lower oxygen content of the oxygen provider thus used for combustion, however, it can still be ensured that the process gas produced has a reduced oxygen content, in particular of less than 10%, so that the process gas can be used for example in coal grinding plants.

According to an advantageous embodiment of the method it is provided that during low-calorific operation air is fed as an oxygen provider for combustion via the first nozzle and a low-calorific combustion gas is simultaneously fed via the second nozzle into the combustion chamber, where they are reacted, in particular combusted. It is hereby made possible to operate a multi-gas burner both with a low-calorific combustion gas and also with a high-calorific combustion gas and not to have to provide a separate burner for each of these operating modes.

This configuration is based upon the recognition that the nozzle which is used in low-calorific operation for the low-calorific combustion gas is not used in the high-calorific operation. This nozzle can thus be used to admix O₂-depleted gas to the air from the first nozzle in order to make the oxygen provider available for combustion. The advantage of this solution in comparison with a provision of a further nozzle for the O₂-depleted gas is that hereby the burner lances used for example only need to have three and not four nozzles. This reduces in particular the construction depth and construction dimensions of a multi-gas burner consisting of one or more such burner lances.

It is preferable if an outer nozzle is selected as the first nozzle, a central nozzle as the second nozzle and an inner nozzle of the burner lance as the third nozzle. Through the outer nozzle, air can thus always be blown into the combustion chamber irrespectively of the low-calorific or high-calorific operation. The combustion gas is blown in during low-calorific operation through a central nozzle so that the combustion gas, after being blown out of the nozzle, is surrounded by the air blown in and is efficiently mixed with it and can react with it. Similarly this is also the case in high-calorific operation, wherein the inner nozzle is used to blow in the high-calorific combustion gas. By using the central nozzle for the O₂-depleted gas it is also possible here for the high-calorific combustion gas blown in through the inner nozzle to efficiently mix with the oxygen provider for the combustion which consists of air and O₂-depleted gas.

The combustion of low-calorific gases is preferably carried out with λ values in the range of from approximately 1.05 to approximately 1.2. Due to the low calorific values, between 2000 kJ/m_(N) ³ and 4000 kJ/m_(N) ³, the combustion temperatures lie below 1300° C. As set out above, during high-calorific operation the multi-gas burner must be operated with higher λ values in order to achieve the necessary reduction in the flame temperature. Depending upon the calorific value of the high-calorific gas used the λ values lie in the range of from approximately 1.5 to approximately 2.0. When combusting coke gas for example the λ value is preferably in the region of 1.6 whereby between 15% and 30% of the oxygen provider for the combustion is O₂-depleted gas.

In order to facilitate the use of the process gas produced in coal grinding plants or other explosion-critical processes, the λ value in low-calorific operation and the λ value as well as the admixing of O₂-depleted gas in high-calorific operation are set in such a way that the hot process gases produced—also described as hot gases—have an O₂ content of less than 10%. Insofar as necessary on the basis of explosion protection directives, a lower target value of the O₂ content in the hot process gas can also be achieved through corresponding adaptation of the admixing of O₂-depleted gas.

In low-calorific operation this can be achieved without significant resources through the comparatively low combustion value of the low-calorific combustion gas.

In high-calorific operation it is necessary in this connection, depending upon the λ value selected, to adequately admix in O₂-depleted gas as a part of the oxygen provider for the combustion. The exact ratio of air to O₂-depleted gas in the oxygen carrier for the combustion depends essentially upon the exactly used high-calorific combustion gas and the λ value then used. It is hereby also possible to achieve oxygen contents in the process gas produced which lie far below 10%.

It is further provided that the quantity of the combustion gas, the λ values and the composition of the oxygen provider for the combustion of air and O₂-depleted gas can be set in such a way that the measured flame temperature does not exceed a value of approximately 1300° C. The λ value is hereby essentially determined by the quantity, that is to say the volume flow per time unit, of the combustion gas and the quantity of the oxygen provider for the combustion, since the proportions of the oxygen provider for the combustion which do not react with the combustion gas contribute to the cooling and reduction of the flame temperature.

According to an advantageous embodiment of the method a recirculated process gas, e.g. from a grinding-drying process, in particular from a coal grinding plant, is used as O₂-depleted gas. In the case of a grinding operation of carbon-containing solid fuels with air conveyance, as is the case for example in air-swept vertical roller mills, a gas must be used as the process gas which has an oxygen content of less than 10%. A so-called grinding-drying process is often hereby carried out, in which the coal to be ground or another starting substance is also dried in addition to being reduced in size. In this connection, as already set out, hot process gases are necessary, but which must have an oxygen content of less than 10% due to explosion protection reasons. These process gases can be diverted from the grinding operation as O₂-depleted gases for the operation of the multi-gas burner. If the hot process gases produced through the multi-gas burner are used for the grinding-drying operation, they are subsequently fed back into the grinding process so that no O₂-depleted process gas is removed in total from the grinding process. It is of course also possible to use O₂-depleted gas from other sources.

According to an advantageous embodiment coking furnace gas is used as high-calorific gas and blast furnace gas as low-calorific gas. Coal grinding plants with a hot gas generator which is constructed from a multi-gas burner are often used within the scope of ore preparation and processing, e.g. smelting processes. Blast furnace gas is produced at the upper edge of the blast furnace, the blast furnace gas being available as a fa-vourable fuel for grinding-drying and the operation of the burner. Any combustion gases such as for example synthesis gas, coke gas or natural gas can be used as high-calorific combustion gases. The low-calorific gas can also be described as lean gas and the high-calorific gas as rich gas. Where reference is made to air within the scope of the invention this can be understood to mean in particular normal ambient air with an oxygen content of approximately 21%. The gases added to the combustion gas within the scope of the combustion process are described within the scope of the invention as oxygen providers for the combustion. Alternatively, the oxygen carrier or provider for the combustion can also be described as combustion air.

Within the scope of the invention a low-calorific gas can be regarded as a gas with a combustion value or calorific value in the range of from approximately 2,000 to 4,000 kJ/m_(N) ³ and a high-calorific gas as a gas with a combustion value or calorific value in the range of from approximately 10,000 to 40,000 kJ/m_(N) ³. It is not hereby entirely significant for the invention which combustion values the low-calorific and the high-calorific gas have but rather that the high-calorific gas has a higher combustion value than the low-calorific gas.

The invention further relates to a multi-gas burner for operation with a low-calorific and a high-calorific combustion gas. In this connection a generic burner having a combustion chamber, at least one burner lance with a first, a second and a third nozzle, having a first, a second and a third feed chamber which are each connected in terms of flow to a respective nozzle in order to feed gases into the combustion chamber, wherein the nozzles terminate with one end in the combustion chamber and with another end in a respective feed chamber and the combustion chambers have a burner muffle in the region of the end of the nozzles, is further developed in that the first feed chamber is designed for feeding an oxygen provider for the combustion. The second feed chamber is designed for feeding the low-calorific combustion gas and O₂-depleted gas. The third feed chamber is designed for feeding the high-calorific combustion gas. Furthermore a feed unit is provided for feeding the low-calorific combustion gas and the O₂-depleted gas into the second feed chamber. The feed unit is designed in such a way that either the low-calorific combustion gas or the O₂-depleted gas is introduced into the second feed chamber in dependence upon the operating mode of the multi-gas burner.

In the case of generic burner lances having at least three nozzles, in most cases in a first operation a nozzle for the oxygen provider for the combustion and a second nozzle for the first combustion gas are used and in a second operation a third nozzle is used for the second combustion gas and furthermore the first nozzle for the oxygen provider for the combustion. In consideration of the idea according to the invention that it is necessary in the combustion of high-calorific gases to operate the multi-gas burner with increased λ values in comparison with a low-calorific operation and consequently that in order to maintain maximum oxygen contents of the heated process gas there is a need to admix O₂-depleted gas to the air, it was hereby recognised that the second nozzle of a burner lance is not used during high-calorific operation in contrast with low-calorific operation and this can thus perform a dual function. This dual function can be seen in the feed of the low-calorific combustion gas in low-calorific operation and the feed of the O₂-depleted gas in high-calorific operation.

In contrast with the use of four nozzles, each of which carries out only a single function, there is hereby the advantage that the multi-gas burner according to the invention has smaller construction dimensions, saves space and investment costs and can be more flexibly used. Material and outlay costs can also be saved as a construction of a burner lance with four nozzles requires more resources than the use of a burner lance with three nozzles.

A burner lance with three nozzles can hereby have an outer pipe, a central pipe and an intermediate pipe arranged between the outer pipe and the central pipe. The pipes are respectively orientated coaxially relative to each other and arranged spaced apart from each other to form annular gaps or flow cross-sections. The burner lance is thus constructed from three pipes coaxially inserted into each other, whereby each flow cross-section thereby produced is connected to a separate feed chamber. The annular gap between the outer pipe and the intermediate pipe forms an outer nozzle, the annular gap between the intermediate pipe and the central pipe forms a central nozzle and the central pipe forms the inner nozzle.

According to an embodiment of the invention the first nozzle is an outer nozzle, the second nozzle is a central nozzle and the third nozzle is an inner nozzle of a burner lance. It is further provided that the first nozzle is connected in terms of flow to the first feed chamber, the second nozzle to the second feed chamber and the third nozzle to the third feed chamber. It is hereby ensured that the air in both low-calorific and high-calorific operation is introduced through the outer nozzle. The low-calorific combustion gas is introduced in low-calorific operation through the adjacent central nozzle and efficient mixing between the combustion gas and the air, which is the oxygen provider for the combustion, is thus facilitated.

Similarly, in high-calorific operation, the air is introduced through the outer nozzle and the O₂-depleted gas through the central nozzle, whereby these can pre-mix with each other. The high-calorific combustion gas is introduced through the inner nozzle. Once again, efficient mixing of the combustion gas with the oxygen carrier for combustion comprising air and O₂-depleted gas is hereby possible.

Furthermore a control unit is provided which is designed in low-calorific operation to introduce air into the first feed chamber, the low-calorific combustion gas into the second feed chamber and to block the supply to the third feed chamber. The control unit is further designed in such a way that in high-calorific operation air is introduced into the first feed chamber, O₂-depleted gas into the second feed chamber and the high-calorific combustion gas into the third feed chamber. Through such a control unit it is ensured that O₂-depleted gas is not wrongly introduced into the second feed chamber in low-calorific operation in addition to the low-calorific combustion gas. This could lead to un-controllable combustion behaviour in the combustion chamber.

The cross-sectional area of the first nozzle relative to the second nozzle and to the third nozzle preferably has a ratio in the range of from 4.4-5.0:5.9-6.3:1, in particular 4.7:6.2:1.The cross-sectional ratios can also be designed to deviate therefrom according to the gas used and depend essentially upon the λ values used, the low-calorific and high-calorific combustion gas, the respective stoichiometric air requirement of the gases and/or the operating or blow-in pressure. Through such a configuration of the cross-sectional areas which essentially determines the possible through-flow of the corresponding gases, it is ensured that sufficient hot gas can be produced with the thus formed multi-gas burner in both operating modes. In particular the design of the second nozzle can be significant for this purpose, as it is used for two different gases, on the one hand low-calorific combustion gas and in the other operating state O₂-depleted gas.

It is advantageous if a plurality of burner lances are provided and the first nozzle of each burner lance is connected in terms of flow to the first feed chamber, each second nozzle is connected in terms of flow to the second feed chamber and each third nozzle is connected in terms of flow to the third feed chamber. A burner lance constitutes in the minimum case a complete multi-gas burner. The desired burner output is achieved through the selection of the number of burner lances. The individual burner lance is standard-ised to a certain output so that, in case of enlargement of the burner, no scale-up needs to be carried out. In this connection reference is made to “numbering-up”, i.e. modified criteria in relation to geometry, flow behaviour, etc. do not have to be considered in each burner configuration. By using a plurality of burner lances in the multi-gas burner it is possible overall to achieve a higher output of the multi-gas burner. In addition by using the burner lance a better regulating behaviour can be achieved. An essential reason for this is the “reciprocal support” of a burner lance bundle, i.e. that the output can be adjusted downwards and the multitude of burner lances serves again and again as an “ignition source”, so that the individual flame does not go out. Regulating ratios of 1:15 are thus possible even with low-calorific gases, although the pre-pressure of the components involved in the combustion lies in the low pressure range.

Due to the fact that only three feed chambers are provided the structure of the multi-gas burner as a whole is simplified.

The invention further relates to a processing plant having a multi-gas burner according to the invention and a grinding plant for solid fuels, e.g. a coal grinding plant. It can in particular be a roller mill, wherein the coal grinding plant is provided as a means to be used as a source for O₂-depleted gas. The O₂-depleted gas can be recirculated process gas from the grinding process, in particular a grinding/drying process. Of course such a configuration can also be used for any other thermal process, i.e. use of a plurality of gases, low O₂ contents in the process gas and use thereof as recirculated gas, high regulating ratios, etc.

By means of a control unit, which can also be designed as a control and regulating unit, the inflows of the different gases, the high-calorific combustion gas, the low-calorific combustion gas, the air and the O₂-depleted gas, can be correspondingly set in dependence upon the operating mode. The control or regulation hereby takes place in such a way that in high-calorific operation the necessary calorific value is achieved with a flame temperature below 1300° C. and with a maximum oxygen content of in particular below 10% of the hot process gas. Similarly, the inflows in low-calorific operation are controlled by the control and regulating unit in such a way that an adequate calorific value is reached without reaching a flame temperature which is too high. When using low-calorific gases the low calorific value necessitates low combustion temperatures so that no significant O₂ problems arise in the process gas here. The respective properties can be fixed in particular by setting the quantities of the gases used and the ratio of the gases to each other.

The invention will be explained below using exemplary embodiments and schematic illustrations, in which:

FIG. 1 shows a simplified structure of a multi-gas burner according to the invention; and

FIG. 2 shows a process diagram of a coal grinding plant with a multi-gas burner according to the invention.

FIG. 1 shows a simplified structure of a multi-gas burner 1 according to the invention. The multi-gas burner 1 shown here has two burner lances 10 which are respectively designed as three-lance burners or three-nozzle lances and have a first nozzle 11, a second nozzle 12 and a third nozzle 13. The burner lances 10 end respectively in a combustion chamber 3.

The multi-gas burner 1 according to the invention further has a first feed chamber 21, a second feed chamber 22 and a third feed chamber 23. The nozzles 11, 12, 13 of the burner lance 10 are formed by three pipes orientated coaxially relative to each other. The first nozzle 11 ends in the first feed chamber 21. The second nozzle 12 ends in the second feed chamber 22 and the third nozzle 13 ends in the third feed chamber 23. The nozzles 11, 12, 13 or the end pipes can hereby be respectively fixed with flange-like connections to the inner wall of the respective feed chambers 21, 22, 23. Furthermore a starting burner 17 is provided in the centre of the multi-gas burner 1 and is used to start the multi-gas burner 1.

Furthermore a feed 31 is provided for the first feed chamber 21, a feed 32 for the second feed chamber 22 and a feed 33 for the third feed chamber 23. Furthermore an ad-ditional fourth feed 34 is provided which also ends in the second feed chamber 22. The feeds 31, 32, 33, 34 have valves which can be controlled via a control unit 36.

The feed 31 is connected to an air source. It is hereby a matter of normal ambient air. The feed line 32 is connected to a source for a low-calorific combustion gas. This can for example be blast furnace gas. Such low-calorific combustion gases are also called lean gases. The feed line 33 is connected to a source for a high-calorific combustion gas which can also be described as a rich gas. The feed line 34 is in turn connected to a source for O₂-depleted gas. This can have in particular an O₂ content of less than 10%.

For low-calorific operation the control unit 36 controls the valves of the feed 31, 32, 33 and 34 in such a way that air flows into the first feed chamber 21 via the feed line 31 and a low-calorific combustion gas flows into the second feed chamber 22 via the feed 32. The other two feed lines 33 and 34 are hereby closed. The ratio of air which flows through the nozzle 11 into the combustion chamber 3 and the low-calorific gas which flows through the nozzle 12 into the combustion chamber 3 is adjusted so that the λ value lies in the range of 1.1.

For high-calorific operation the control unit 36 opens the valves of the feed lines 31, 33 and 34. Air hereby flows into the feed chamber 21, O₂-depleted gas into the feed chamber 22 and high-calorific gas into the feed chamber 23. By means of the nozzles 11, 12, 13 these gases can flow into the combustion chamber 3 and react with each other there.

The control unit 36 hereby controls the inflow of air, of the O₂-depleted gas and the high-calorific combustion gas in such a way that a λ value in the region of 1.6 is set, whereby approximately 30% of the oxygen carrier for the combustion is O₂-depleted gas. At the end of the burner lance 11 on the combustion chamber side, swirl means can be provided in the region of the respective end of the nozzles in order to efficiently mix the out-flowing gases with each other.

Alternatively to the feed 34, other embodiments are also possible, in which the chamber 22 can be supplied both with the low-calorific combustion gas and with the O₂-depleted gas. For example it is conceivable to be able to introduce via the feed 32 both low-calorific gas and also O₂-depleted gas. This can be facilitated by a corresponding feed line and a three-way valve. In this case the feed line 34 can be omitted.

FIG. 2 shows a process diagram of a coal grinding plant with a hot gas generator which uses a multi-gas burner 10 according to the invention.

A central element of the processing plant set out here is on the one hand the mill-classifier combination 52, which can for example be a vertical roller mill with recirculating air operation, in particular a LOESCHE roller mill. On the other hand a hot gas generator 51 is provided which has a multi-gas burner 10 according to the invention. The hot gas generator 51 serves to produce hot process gases or respectively to heat them, whereby these process gases are used within the scope of the grinding process in the mill-classifier combination 52 in order to dry the material to be ground, in this case raw coal, in addition to the grinding process. For this purpose a hot gas feed 54 is provided between the hot gas generator 51 and the mill-classifier combination 52.

A coal grinding plant is to be regarded here merely as an example for a processing plant, in which a hot gas generator 51 is used. Instead of a mill-classifier combination 52, other plant components can also be provided, in which generated hot process gas is used.

The raw coal to be ground is fed via a coal bunker 61 to the mill-classifier combination 52. In the mill-classifier combination 52 the raw coal is ground to dust and dried with the aid of the hot gas which flows via the feed 54 into the mill-classifier combination 52, is dried and transported in the direction of a filter 62 by means of air flow.

In the filter 62 the carbon dust produced is separated and fed to a dust bunker 63. The carbon dust can then be removed from the dust bunker 63 and fed for its use, for example for PCI processes. The process gas purified from the dust, which process gas has also cooled in the meantime, is once again fed via a process gas recirculation means 56 to the hot gas generator 51. It is heated here by the combustion energy and fed back via the hot gas feed 54 to the mill-classifier combination 52.

The multi-gas burner 10 of the hot gas generator 51 has four different feeds. Feed 71 serves for the feed of a low-calorific combustion gas, for example blast furnace gas, feed 72 for the feed of air, feed 73 for the feed of a high-calorific combustion gas, for example coke gas, and feed 74 for the feed of gas to the starting burner. Natural gas can be used for example for this purpose.

In order to also be able, according to the method according to the invention, to admix O₂-depleted gas to the air when firing the multi-gas burner with the high-calorific gas, it is further provided to provide a recirculated gas branch element 57 in the process gas recirculation 56. This branch element 57 ends at a recirculated gas feed 76 which ends in the feed line for the low-calorific combustion gas.

It is thus possible, in dependence upon the selected operating mode of the multi-gas burner 10 of the hot gas generator 1, to feed the low-calorific combustion gas via the feed 71 or recirculated gas as O₂-depleted gas which is recovered from the recirculated process gas. This recirculated process gas is also referred to as recirculated gas.

It is thus possible with the method according to the invention and the multi-gas burner according to the invention to use both low-calorific gases and also high-calorific gases while complying with environmental and safety legislation for the generation of hot process gases. 

1. Method for operating a multi-gas burner in low-calorific operation with a low-calorific combustion gas and in a high-calorific operation with a high-calorific combustion gas, wherein the multi-gas burner has at least one burner lance with a first, a second and a third nozzle, a first, a second and a third feed chamber which are each connected in terms of flow to a respective nozzle and a combustion chamber, into which the at least one burner lance projects, characterised in that in a high-calorific operation air is fed via the first nozzle and simultaneously O₂-depleted gas via the second nozzle and a high-calorific combustion gas via the third nozzle into the combustion chamber, where they are reacted, in particular combusted, the air and the O₂-depleted gas being used as oxygen carriers for the combustion and in a low-calorific operation air is fed via the first nozzle as an oxygen carrier for the combustion and simultaneously a low-calorific combustion gas is fed via the second nozzle into the combustion chamber, where they are reacted, in particular combusted.
 2. Method according to claim 1, characterised in that an outer nozzle is selected as a first nozzle, a central nozzle as a second nozzle and an inner nozzle as a third nozzle.
 3. Method according to claim 1, characterised in that the multi-gas burner is operated in low-calorific operation with a λ value in the range of from approximately 1.05 to approximately 1.2.
 4. Method according to claim 1, characterised in that the multi-gas burner is operated in high-calorific operation with a λ value of from approximately 1.4 to approximately 2.0, wherein approximately 15% to 30% of the oxygen provider comes from the O₂-depleted gas.
 5. Method according to claim 1, characterised in that the λ value in low-calorific operation and the λ value and the mix of O₂-depleted gas in high-calorific operation are set in such a way that the hot gases have an O₂ content of less than 10%.
 6. Method according to claim 1, characterised in that the quantity of the combustion gas, the λ value and the composition of the oxygen carrier for the combustion from air and O₂-depleted gas are set in such a way that a flame temperature of 1300° C. is not exceeded.
 7. Method according to claim 1, characterised in that a recirculated process gas from a grinding operation, in particular a grinding plant for solid fuels, is used as O₂-depleted gas.
 8. Method according to claim 1, characterised in that coke furnace gas is used as high-calorific gas and blast furnace gas as low-calorific gas.
 9. Multi-gas burner for a low-calorific operation with a low-calorific combustion gas and for a high-calorific operation with a high-calorific combustion gas, having a combustion chamber, at least one burner lance, with a first, a second and a third nozzle, a first, second and third feed chamber which are each connected in terms of flow to a respective nozzle for feeding gases into the combustion chamber, wherein the nozzles terminate with one end in the combustion chamber and with another end in a respective feed chamber, wherein the combustion chamber has a burner muffle in the region of the end of the nozzles, wherein the first feed chamber is designed for feeding of an oxygen carrier for combustion and wherein the third feed chamber is designed for feeding of the high-calorific combustion gas, characterised in that the second feed chamber is designed for feeding of the low-calorific combustion gas and O₂-depleted gas and a feed unit for feeding the low-calorific combustion gas and the O₂-depleted gas into the second feed chamber, which is designed to introduce either the low-calorific combustion gas or the O₂-depleted gas, in dependence upon the operating mode of the multi-gas burner, into the second feed chamber.
 10. Multi-gas burner according to claim 9, characterised in that the first nozzle is an outer nozzle, the second nozzle is a central nozzle and the third nozzle is an inner nozzle of the burner lance, the first nozzle is connected in terms of flow to the first feed chamber, the second nozzle is connected in terms of flow to the second feed chamber, the third nozzle is connected in terms of flow to the third feed chamber.
 11. Multi-gas burner according to claim 9, characterised in that a control unit is provided which is designed, during low-calorific operation, to introduce air into the first feed chamber, the low-calorific combustion gas into the second feed chamber and to block the feed to the third feed chamber, and the control unit is designed, during high-calorific operation, to introduce air into the first feed chamber, O₂-depleted gas into the second feed chamber and the high-calorific combustion gas into the third feed chamber.
 12. Multi-gas burner according to claim 9, characterised in that a ratio of the cross-sectional areas of the first to the second to the third nozzle is dependent upon the λ values used, the low-calorific and high-calorific combustion gas and/or the respective stoichiometric air requirement, and lies in particular in the region of approximately 4.5-4.9:6.0-6.4:1.
 13. Multi-gas burner according to claim 9, characterised in that a plurality of burner lances are provided and each first nozzle is connected in terms of flow to the first feed chamber, each second nozzle to the second feed chamber and each third nozzle to the third feed chamber.
 14. Processing plant, having a multi-gas burner according to claim 9 and a thermal process, wherein recirculated process gas from the thermal process is used as O₂-depleted gas. 